Long-short separator for serially conveyed units



Wired 4 Stat Paw O" LONG-SHORT SEPARATOR FOR SERIALLY CONVEYED UNITSGregory J. Harmon, Bethesda, Md., assignor to Reed Research, Inc.,Washington, D.'C., a corporation of Delaware Filed May13, 1 955,Ser.No.508,069 l 4 Claims. Cl. 209-82) sensing. machine of the typedescribedin;copending applications, Serial Number 460,385, filed October 5, 1954,for Stamp Sensing Letter Sorter, now Patent No. 2,93 6,- 886, issued May17, 1960, and Serial Number 478,694, filed December 30, 1954, forArticle Handling andSorting Apparatus. t

It is a primary object of the invention to sort'all pieces Patented May2, 1961 ice tion A, the path of the letter, indicated by arrow, I

crossed by a narrow beam of light from lamp 4 which is directed into aphotocell 2. A similar lamp 5 and photocell 3 at station B provide asecond sensing device. It is preferable that the light sources furnishlight beams of constant intensity such that the beams do not cause theoutput currents of 2 and 3 to be modulated appreciably.

The sequence of events when aletter progresses through 1 in thedirection shown in Fig. 1 is then as follows: ConsideringphotocellZonly, a steep voltage rise occurs in the output circuit 'of 2just.as theleadingedge 8 of letter '6. interrupts the light beam from lamp 4 attime t The increased voltage is sustained until trailing edge 7 of theletter emerges from theflight -beamat time t The output circuit of 2then registers an abrupt voltage drop to the initial starting voltage.Since S and 5 are identical with 2 and 4 in all respects, includingassociated load circuits, etc., a second voltage excursion, identicalinpolarity andmagnitude to that obtained in the load circuit of 2, occursin the output circuit of.3 as letter 6 passes through the light beamfromlamp 5. In Fig. 1, times t and 1 represent, respectively, the instantsat which letter edges 8 bearnB. v y

Now, while t always marks a later point in timethan t t;, or 1 and t5 isalways later than t t is not necesof mail which are not greater than apermissible maximum length into one conveyer channel, hereafter calledthe short channel, for further'treat-ment and to sort all items whichare greaterthan said permissible length into another channel which maybe termed the long, channel. Another object is to provide asorting-device of the above type which is substantially independent ofthe gap between successive units, although 'it will be apparent'that acertain minimum gap must exist between units so that they can bedistinguished at all by their length.

Another object is to provide electrical means for sorting seriallyconveyed spaced units, such as pieces of mail, according to lengthdirectly without the use of reference time-basis or markers such aselectronically generated gates contained within the circuitry. 4

Another object is to provide a simple and fool-proof length sorter whichis positive and definite in its action under all practical conditions.

According to the invention, passage of a conveyed unit past two spacedsensing stations causes a beam of light shining into a photocell at eachstation to be successively interrupted and reestablished, to produce ateach station a voltage pulse having a leading and a trailing edge. The

circuit is so arranged that the time of the leading edge at the forwardstation is compared with the time of the trailing edge at the rearwardstation and the latter of these two times determines which channel willbe selected.

The specific nature of the invention, as well as other objects andadvantages thereof, will clearly appear from a description of apreferred embodiment as shown in the accompanying drawing, in which:

Fig. l is a schematic drawing showing the principle of the invention;and

Fig. 2 is a circuit diagram of a practical circuit for carrying out theinvention of Fig l.

Referring to Fig. 1, the distance gage 1 contains two stations A and Bseparated by a distance corresponding to the desired critical length.Letters greater than this length are to be directed into onefchannel andshorter.

letters are to be directed into another channel. At stasarily later thanAssume .thecase in which the length of letter, 6 measured fromedge'7 toedge 8 is sufficiently great to intercept the light beams at bothstations A and B simultaneously. Then, it is apparent from Fig. 1 thatas the letter travels in the direction indicated, edge 8 will enter thelight beam at station E before edge 7 leaves the light beam at stationA. In this-case t occurs earlier in time than t and the letter isdesignated as a long. Conversely, if the letter has insufficient lengthto interrupt the light beams at both stations Aand B simultaneously and,travels as shown, t will be delayed in time be'yond t and the letter isdesignated as a short. 1

By making use of the fact that t and t are interchangeable in time,depending on the lengths of the letters passed, a two-channel circuitmay be arranged to cause polarities in Which they are delivered from thedifierentiator of 9. Elements 12 and 13 of Fig. 1 are thyratrons andform the two symmetrical halves of a bistable trigger circuit. That is,12 will remain in a stable state, conducting current, with 13 renderednon-conducting, or vice versa. The circuitry is so arranged that onlypositive voltage pulses such as those at t or t will cause I triggering,12 and 13 remaining unresponsive to negative pulses such as those-at tor 1 At the instant when a pulse at t causes 12 to conduct, anenergizing current flows through the coil of relay 14 from the outputcircuit of 12 releasing an escapement or latch attached to the relayarmature. The unlatching action permits pivoted and spring-retained gatedoor 16 to open under the impact of moving letter 6.

Channel II functions in entirely the same manner as channel I with theexception that 10, which is the exact counterpart of 9, is followed by apulse-inverting circuit, 11. This is essential since the desiredmeasurement pulse at 1' is delivered from 10 with negative polarity andand 7 enter, and emerge from,

must be positive when applied as a trigger at the input of 13. Becauseof the bistable action of 12 and 13, it is impossible for gate 17 toswing open when 12 is conducting or for gate 16 to open when 13 isconducting. In other words, gate 16, only, is open for a long letterwith 17 closed, the reverse condition obtaining for a short letter.

It is clear then, that the sole determining factor in the routing ofletters through paths 18 or 19 is the priority of occurrence of pulsesat t or t Any letter passed through 1 in Fig. 1 will cause both 12 and13 to be triggered by pulses at t and t respectively. If the letter is along, the determining pulse occurs at t since t in that case causes thelast positive pulse set off by that letter to reach the trigger circuit.If the letter is a short, the determining pulse is at t since 12 thenbecomes the last positive pulse in the train. Thus, all longs are routedthrough path 18 and all shorts through 19.

Fig. 2 shows the details of a practical circuit in accordance withFig. 1. Corresponding elements are given the same reference character asin Fig. l with a prime added. The plate voltage level of amplifier tube9' is normally low since the tube is biased to conduct when the lightbeam at station A reaches photocell 2. Upon interruption of the beam bythe leading edge 8' of letter 6', the grid bias of tube 9' goes negativeand cuts off the tube, causing the plate voltage of tube 9 to rise andpassing a positive pulse to the primary of pulse transformer 20 throughthe resistance of potentiometer 26, which is adjustable so that theamplitude can be varied, and thence through condenser 22 to the primaryof pulse transformer 20. The condenser, together with the inductance andinherent resistance of the transformer, act as a conventionaldifferentiating circuit to produce a sharp positive pulse in the primaryof the transformer. The transformer secondary winding is so connected tothe grid of thyratron 12' that a positive pulse in the primary producesa negative pulse in the secondary circuit which is applied to the grid.Similarly, when the letter passes station A, its trailing edge 7'produces the opposite effect throughout the foregoing circuit, resultingin a positive pulse at the grid of thyratron 12' at time t Dampingresistor 56 is connected across the secondary of transformer 20 toprevent a large overshoot or oscillation in the opposite direction fromthe initial pulse, which might cause improper operation, it beingdesirable to have a single strong positive pulse occur only when thetrailing edge passes station A. The magnitude of the pulse can, ofcourse, be controlled by the setting of potentiometer 26.

At station B, the same effects occur, except that the opposite terminalof the secondary of transformer 11 is applied to the control grid ofthyratron 13', so that the leading edge, rather than the trailing edge,produces the positive pulse to trigger thynatron 13'. Thus the actiondescribed in connection with Fig. 1 is produced. The plate circuits ofthyratrons 12' and 13' are coupled through condenser 30 to produce thewell-known bistable trigger circuit action whereby the last energizedthyratron remains conducting until a sufliciently positive voltage isapplied, which may be in the form of a brief pulse, to the grid of theother thyratron, which reverses the condition. Each thyratronactuatesits associated gate magnet 14 and 16 respectively to control the routingof the mail.

The power supply for the foregoing circuit is preferably regulated andmay comprise transformers 36 and 38, the latter furnishing the filamentsupply for the rectifier tube (5690) and the grid bias for thethyratrons through a suitable ballast (7T1H) to insure that the correctbias values will be maintained under all ordinary conditions of linevoltage. Similarly, transformer 36 furnishes the remaining filamentsupplies and the plate voltage supplies through filter circuit 40 andgas diode 42 (type 0D3W). In normal operation the gas tube fires anddraws a bleeder current through 7500 ohms resistor 44 as a ballastcurrent. If the current through the load tends to change so as to drawmore or less current, the gas tube tends to compensate so that it drawsless current as the circuit draws more, and vice-versa.

It will be apparent that instead of interrupting a beam of light by thepassage of the letter, the reflection of a beam of light from the lettercould be used to operate the photocells at stations A and B. Likewise,it will be apparent that the polarities shown are given by way ofexample only, and that the operative polarities could be reversed by theuse of suitable circuitry. Similarly, other types of bistable triggerscould be used than the one shown.

In order to clarify the operation of applicants apparatus and claim thecombinations thereof in terms of the functional relationships disclosedabove, the following terms are defined: the bistable trigger meanscomprises elements 12', 13', 30, and their associated connections asshown in Figure 2; the gate control means comprises elements 12', 13',30, 32, 34, 14', 15', and their associated connections as shown inFigure 2; the condition ing circuit means comprises elements 9', 10',20, 11, 22, 24, 26, and their associated connections as shown in Figure2; and the gate operating circuits comprise (l) elements 32, 14', andtheir associated power supply as shown in Figure 2 and (2) elements 34,15, and their associated power supply as shown in Figure 2.

It will be apparent that the embodiments shown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of my invention is defined in the appended claims.

I claim:

1. In apparatus for sorting serially conveyed units according to length,the combination comprising; means for conveying a series of separateunits in a predetermined path of motion, said path of motion having adirection, said units spaced by a predetermined minimum gap in thedirection of said path of motion, each of said units having a leadingedge and a trailing edge, said units oriented so that their leadingedges traverse said path in advance of their trailing edges, a firstsensing station positioned adjacent to said conveying means, said firstsensing station comprising means for producing one electrical signalinitiated by the passage of the trailing edge of a unit past said firststation, a second sensing station positioned adjacent to said conveyingmeans and spaced from said first sensing station forwardly along thedirection of motion of said units by a predetermined distancecorresponding to a critical length of said units, said second sensingstation comprising means for producing another electrical signalinitiated by the passage of the leading edge of a unit past said secondstation, two channels positioned adjacent to said conveying means andspaced forwardly of both of said first and second stations with respectto said direction of motion of said units, selector gate meanspositioned adjacent to said conveying means and operatively associatedwith said means for producing said one electrical signal and saidanother electrical signal at said first and second stations and said twochannels, said gate means having two positions for directing said unitsto one of said two channels after said units have traversed both of saidstations, bistable trigger means connected to each of said signalproducing means, said trigger means having two alternative stablepositions, electrical differentiating circuit means connected to each ofsaid signal producing means for difierentiating said electrical signalsand thereby producing sharp electrical pulses of one polaritycorresponding to a leading edge signal from each of said signalproducing means and sharp electrical pulses of the polarity opposite tosaid one polarity corresponding to a trailing edge signal from each ofsaid signal producing means, means for inverting the polarity of theelectrical signals a from one of said signal producing means connectedto one of said differentiating circuit means so that the leading edgesignal from said signal producing means of said second station is of thesame polarity as the trailing edge signal from said signal producingmeans of said first station, and means for connecting said means forinverting of the one circuit, and said diiferentiating circuit means ofthe other circuit to said bistable trigger means for triggering saidbistable means to one of said two stable positions with either saidsecondstation leading edge pulse signal or said firststation trailingedge pulse signal, whereby the latest in time of said last two signalsdetermines the position of said selector gate means.

2. The invention according ,to' claim 1, said bistable trigger meanscomprising two thyratron trigger tubes electrically connected to haveopposite and mutually excl-n sive conduction states.

3. The invention according to claim 2, said polarity inverting meanscomprising at least one pulse transformer having windings oriented toproduce pulse polarity inversion.

4. In apparatus for sorting serially conveyed units according to length,the combination comprising; means for conveying a series of separateunits in a fixed path of motion, said path of motion having a direction,said units spaced by a predetermined minimum gap in the direction ofsaid path of motion, only two sensing stations spaced along said meansfor conveying and consisting of a first station and a second stationspaced from said first station forwardly along the direction of motionof said units by a predetermined distance corresponding to a criticallengthof said units, two channels positioned adjacent to said means forconveying and spaced forwardly of both said first and second stationswith respect to the direction of motion of said units, selector gatemeans operative to allow communication between said path and one of saidtwo channels, each of said first and second stations comprising anelectrical sensing means connected in an electrical signal circuit andoperable during the time of passage of any of said units past saidstation to produce an electrical signal in its associated signalcircuit, selector gate control means operatively associated with saidelectrical sensing means of the signal circuits of said first and secondstations to condition one of said two gate operating circuits foroperation in the absence of a signal from said electrical sensing meansof said first station caused by'a trailing edge of a unit at the timewhen the leading edge of the same unit reaches said electrical sensingmeans of said second station and causes a signal, and for laterconditioning the other of said two gate operating circuits for operationand returning said first conditioned circuit back to a non-conditionedstate when the signal caused by the trailing edge of the same unitpasses said electrical sensing means of said first station, whereby onlythe conditioned one of said two gate operating circuits is actuated uponthe leading edge of a unit reaching said electrical sensing means ofsaid second station.

References Cited in the file of this patent UNITED STATES PATENTS1,998,950 Cockn'll ..Apr. 23, 1935 2,033,645 Parkhill Mar. 10, 19362,085,671 1 Powers June 29, 1937 2,162,508 Knowles June 13, 19392,415,176 Hurley Feb. 4, 1947 2,415,177 Hurley Feb. 4, 1947 2,602,847Larew July 8, 1952 2,630,043 Kolisch Mar. 3, 1953 2,740,521 Calvin Apr.3, 1956 2,933,185 Coleman et a1. Apr. 19, 1960 FOREIGN PATENTS 682,303Great Britain Nov. 5, 1952 OTHER REFERENCES Circuit Theory of ElectronDevices, pages 178 to 186, John Wiley and Sons, Inc., copyright 1953..(Copy in Patent Ofiice Library).

